Potable water producing utilities disinfect the water by the addition of halogenating agents (halo is a prefix for chlorine, bromine and iodine). While these agents are beneficial to killing illness bearing microorganisms, they unfortunately also produce various halogenated disinfection by-products (DBPs) such as trihalomethanes (THMs), haloacetic acids, haloaldehydes, haloacetones, haloacetonitriles and chloral hydrate. THMs, in particular, head the USA EPA list of toxic and carcinogenic compounds highly regulated in drinking water. THMs as a group include chloroform (CHCl3), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3). These 4 THMs are included among the 25 volatile organic compounds regulated under the Safe Drinking Water Act (SDWA) of 1974.
In 1979, the US Environmental Protection Agency (EPA) set the maximum total contaminant level of 100 parts per billion (ppb) for the 4 THMs. The Stage 1 Disinfectant and Disinfection Byproduct Rule announced in 1998 updates and supersedes the 1979 regulations for total trihalomethanes by lowering the total THMs regulatory limit to 80 ppb. Recently the American Water Works Association (AWWA) data base reported that a safety margin of 15% below the regulatory limit for total THMs should be targeted. The Safe Drinking Water Act (SDWA) in 1996 requires the EPA to develop rules to balance the risks between microbial pathogens and disinfection byproducts (DBPs). It is important to strengthen protection against microbial contaminants, and at the same time, reduce the potential health risks of DBPs.
Subsequently, various methods and apparatus were developed for the measurement of halohydrocarbons, especially THMs, in aqueous solutions. Traditional analytical methods used to quantify THMs in water are based upon gas chromatography (GC) equipped with an electron capture detector (ECD) or a mass-spectrometer (MS). In this method, water samples are typically collected in vials and brought to an offsite laboratory to analyze by GC-ECD or GC-MS. Individual compounds are determined and the sum of all 4 THMs constitute total THMs (TTHM). This process is very laborious and time consuming.
In the literature, a simpler chemical method cited to determine total THMs in water is based upon colorimetric determination. In this method, when pyridine is reacted with THMs in a strong alkaline solution, a red color is formed. The intensity of the color is determined using an optical spectrometer. The color intensity produced is proportional to the total amount of THMs present in the sample. This method is called the “Fujiwara reaction” (K. Fujiwara, Sitzfer, Aohandl. Naturforsch. Ges. Rostock, 6, 33, 1941; G. A. Lugg, Anal. Chem., 38, 1532, 1982; T. Uno et al. Chem. Pharm. Bull., 30, 1876, 1982).
Fujiwara reactions can, however, present certain problems, as pyridine can be insoluble in some reagents used to make the medium alkaline. For example, when using an inorganic base such as NaOH or KOH, it is difficult to diffuse OH− ions from the aqueous phase into the pyridine organic phase. Since the diffusion of OH− ions is difficult to control, the results are not easily reproducible.
Most of the above methods and apparatus described in the literature for measurement of halohydrocarbons require expensive equipment, itself with substantial maintenance demands, extensive personnel training, and significant turn-round time (12-24 hours), or expose the operator to noxious chemicals. The present invention addresses the need for a low cost, simple, reliable, automated and on-line real-time method to measure THMs in water.